Mixed antimony oxide-cerium oxide oxidation catalysts



oxide or oxides.

United States Patent 3,2b0,034 MIXED ANTIMONY fiXlDE-CERIUM (PXIDEOXIDATEON CATALYSTS James L. Callahan, Redford, Ohio, and BertholdGertisser,

New York, N.Y., assignors to The Standard Oil Company, Cleveland, Uhio,a corporation of Ohio No Drawing. Filed Oct. 15, 1962, Ser. No. 230,7176 Claims. -(Cl. 252-462) This invention relates to oxidation catalystsystems consisting essentially of oxides of antimony and cerium and tothe catalytic oxidation of olefins to oxygenated hydrocarbons such assaturated aldehydes, for example, propylene to acrolein, and to theoxidation of olefin-ammonia mixtures to unsaturated nitriles, such aspropyleneammonia to acrylonitrile, using such systems.

US. Patent No. 2,904,580 dated September 15, 1959, describes a catalystcomposed of antimony oxide and molybdenum oxide, as antimony molybdate,andindicates its utility in converting propylene to acrylonitrile.

British Patent 864,666 published April 6, 1961, describes a catalystcomposed of an antimony oxide alone or in combination with a molybdenumoxide, a tungsten oxide, a tellurium oxide, a copper oxide, a titaniumoxide, or a cobalt oxide. These catalysts are said to be either mixturesof these oxides or oxygen-containing compounds of antimony with theother metal, such as antimony molybdate or molybdenum antimonate. Thesecatalyst systems are said to be useful in the production of unsaturatedaldehydes such as acrolein or methacrolein from olefins such aspropylene or isobutene and oxygen.

British Patent 876,446 published August 30, 1961 describes catalystsincluding antimony, oxygen and tin, and said to be either mixtures ofantimony oxides with tin oxides, or oxygen-containing compounds ofantimony and tin such as tin antimonate. These catalysts are said to beuseful in the production of unsaturated aliphatic 1 nitriles such asacrylonitrile from olefiins such as propylene, oxygen and ammonia.

I. THE CATALYST In accordance with the invention, an oxidation catalystis provided consisting essentially of oxides of antimony and cerium.This catalyst is useful not only in the oxidation of olefins tooxygenated hydrocarbons such as acrolein and the oxidation ofolefin-ammonia mixtures to unsaturatednitriles such as acrylonitrile,but also in the catalytic oxidative dehydrogenation of olefins todiolefins.

The nature of the chemical compounds which compose the catalyst of theinvention is not known. The catalyst may be a mixture of antimony oxideor oxides and cerium It is also possible that the antimony and ceriumare combined with the oxygen to form a cerium antimonate.. X-rayexamination of the catalyst system has indicated the presence of astructurally common phase of the antimony type, composed of antimonyoxide, and some form of cerium oxide. Antimony tetroxide has beenidentified as present. For the purposes of description of the invention,this catalyst system will be referred to as a mixture of antimony andcerium oxides, but this is not to be construed as meaning that thecatalyst is composed either in whole or in part of these compounds.

The proportions of antimony and cerium in the catalyst system may varywidely. The Sb:Ce atomic ratio can range from about 1:50 to about 9951.However, optimum activity appears to be obtained at SbzC-e atomic ratioswithin the range from 1:1 to 25:1.

The catalyst can be employed without support, and

.will display excellent activity. It also can be combined With asupport, and preferably at least 10% up to about 90% of the supportingcompound by weight of the entire ice composition is employed in thisevent. Any known support materials can be used, such as, for example,silica, alumina, zirconia, alundum, silicon carbide, aluminasilica, andthe inorganic phosphates, silicates, aluminates, borates and carbonatesstable under the reaction conditions to be encountered in the use of thecatalyst.

The antimony oxide and cerium oxide can be blended together, or can beformed separately and then blended, or formed separately or together insitu. As starting materials for the antimony oxide componenafor example,there can be used any antimony oxide, such as antimony trioxide,antimony tetroxide and antimony pentoxide, or mixtures thereof; or ahydrous antimony oxide, metaanti-monic acid, orthoantimonic acid orpyroantimonic acid; or a hydrolyzable or decomposable antimony salt,such as an antimony halide, for example, antimony 'trichloride,trifluoride or tribromide; antimony pentachloride and antimonypentafluoride, which is hydrolyzable in Water to form the hydrous oxide.Antimony metal can be employed, the hydrous oxide being formed byoxidizing the metal with an oxidizing acid such as nitric acid. y y r.

The cerium oxide components can be provided in the form of cerous oxide,ceric oxide, or ceric peroxide, or by precipitation in situ from asoluble cerium salt. such as the nitrate, acetate, or a halide such asthe chloride.

Metallic cerium can be used as a starting material, and if antimonymetal is also employed, the antimony can be converted to the oxide andthe cerium to the nitrate simultaneously by oxidation in hot nitricacid. A slurry of hydrous antimony oxide in nitric acid can be combinedwith a solution of a cerium salt such as diammonium ceric nitrate, whichis then precipitated in situ as the hydroxide by making the solutionalkaline with ammonium hydroxide, the ammonium nitrateand the otherammonium salts being removed by filtration of the resulting slurry.

It will be apparent from the above that cerous carbonate, cerousbromide, cerous bromate, cerous chloride, cerous fluoride, cerousiodide, cerous molybdate, ceric hydroxy nitrate, cerous acetate, ceroussulfate, ceric sulfate, cerous phosphate, ceric hydroxide, cerousformate and cerous hydroxide can be employed as the source of the ceriumoxide component.

The catalytic activity of the system is enhanced by heating at anelevated temperature. Preferably, the catalyst mixture is dried andheated at a temperature of from about 500 to about 1150 F. preferably atabout 700m 900 F., for from two to twenty-four hours. If activity thenis not sufficient, the catalyst can be further heated at a temperatureabove about 1000 F. but below a temperature deleterious to the catalystat which it is melted or decomposed, preferably from about 1400 F. toabout 1900 F. for from one ;to forty-eight hours, in the presence of airor oxygen. Usually this limit is not reached before 2000 F. and in somecases, this tember, permitting circulation of air or oxygen, so that anyoxygen consumed can be replaced. I

The antimony oxide-cerium oxide catalyst composition of the inventioncan be defined by the following empirical formula:

SbgCe O Where a is '1 to 99, b is 50 to 1, and c is .a number taken tosatisfy the average valences of antimony and cerium in the oxidationstates in which they exist in the catalyst as defined by the empiricalformula rabove. Thus, the Sb valence may range from 3 to 5 and the Cevalence from This catalyst sytem is useful in the oxidation of olefins"to oxygenated compounds, such as aldehydes, in the presence of oxygen,and in the oxidation ofolefins to unsaturated nitriles in the presenceof oxygen and ammonia. Both nitril-es and a-ldehydes can be producedsimultaneously using process conditions Within the overlapping rangesfor these reactions, as set forth in detail below. The term oxidation asused in this specification and claims encompasses the oxidation toaldehydes and to nitriles, both of which require oxygen as a reactant.

II. OXIDATION OF OLEFINS TO ALDEHYDES The reactants used in theoxidation to oxygenated compounds are oxygen and an olefin having onlythree carbon atoms in \a straight chain such as propylene orisobutylene, or mixtures thereof.

The olefins may be in admixture with parafiinic hydrocarbons, such asethane, propane, butane and pentane, for

example, a propylene-propane mixture may constitute the atmospher-icpressures, e.g., above '100 p.s.i.g. are employed, somewhat lowertemperatures are feasible. In the case where this process is employed toconvert propylene to acrolein, a temperature range of 750 to 950 'F. hasbeen found to be optimum at atmospheric pressure.

While pressures other than atmospheric may be employed, it is generallypreferred to operate at or near atmospheric pressure, since the reactionproceeds well at 'such pressures and the use of expensive high pressureequipment is avoided. V

The apparent contact time employed in the process is not critical and itmay be selected from a broad operable range which may vary from 0.1 to50 seconds. The apparent contact time may be defined as the length oftime 1n seconds whichthe unit volume of gas measured under theconditions of reaction is in contact with the apparent unit volume ofthe catalyst. It may be calculated, for exam.- ple, from the apparentvolume of the catalyst bed, the average temperature and pressure of thereactor, and the how rates of the several components of the reactionmixfrom.

The optimum contact time will, of course, vary, depending upon theolefin being treated, but in the case of propylene the preferred contacttime is 0.5 to seconds.

A molar ratio of oxygen to olefin between about 0.5:1

'to '5 :1 generally gives the most satisfactory results. For

the conversion of propylene .to acrolein, a preferred ratio of oxygen toolefin is from about 1:1 to about 2:1. The oxygen used in the processmay be derived from any source; however, air is the least expensivesource of oxygen, and is preferred for that reason.

We have also discovered that the addition of water to the reactionmixture has a marked beneficial influence on V the course of thereaction in that it improves the conversion and the yield of the desiredproduct. The manner in which water affects the reaction is not fullyunderstood but the theory of this phenomenon is not deemedimportant inview of the experimental results we have obtained. Accordingly, weprefer to include water in the reaction mixture. Generally, a ratio ofolefin. to water in the reaction mixture of from 1:0.5 to -1:l0 willgive very satisfactory results, and a ratio oflfrom 1:0.75 to 1:6 hasbeen and these materials can be present. Consequently, the addition ofsaturated hydrocarbons to the feed to the found to be optimum whenconverting propylene to acrolein. The water, of course, will be in thevapor phase during the reaction.

Inert diluents such :as nitrogen and carbon dioxide may be present inthe reaction mixture.

In general, any apparatus of the type suitable for carrying outoxidation reactions in the vapor phase may be employed for the executionof the process. The process may be operated continuously orintermittently, and may employ a fixed bed with a large particulate orpelleted catalyst, or a so-called fluidized bed of catalyst. Thefluidized bed permits a closer control of the temperatures of thereaction, as is well known to those skilled in the art, and'a fixed bedgives closer control of contact time.

The reactor may be brought to the reaction temperature before or afterthe introduction of the vapors to be reacted. In a large scaleoperation, it is preferred to carry out the process in a continuousmanner and in this system the recirculation of unreacted olefin and/ oroxygen is contemplated. Periodic regeneration or reactivation of thecatalyst is also contemplated. This may be accomplished, for example, bycontacting the catalyst with air at an elevated temperature.

T he unsaturated carbonyl product or products may be isolated from thegases leaving the reaction zone by any appropriate means, the exactprocedure in :any given case being determined by the nature-and quantityof the reaction products. For example, the excess gas may be scrubbedwith cold waterlor an appropriate solvent to remove the carbonylproduct. In the case where the products are recovered in this manner,the ultimate recovery from the solvent may be by any suitable means suchas distillation. The efiiciency of the scrubbing operation may beimproved when water is'employ ed as the scrubbing agent by adding asuitable wetting agent to the water. If

desired, the scrubbing of the reaction gases may be preceded by a coldwater quench of the gases which of itself will serve to separate asignificant amount of the carbonyl products. Where molecular oxygen isemployed as the oxidizing agent in this process, the resulting productmiX- ture remaining after the removal of the carbonyl product 'may betreated to remove carbon dioxide with the remainder of the mixturecomprising any unreacted olefin an oxygen being recycled through thereactor. In the case where air is employed as the oxidizing agent inlieu of molecular oxygen, the residual product after separation of thecarbonyl product may be scrubbed with a non-polar solvent, e.g., 1ahydrocarbonfraction, in order to uncover unreacted olefin and in thiscase the remaining gases may be discarded. I An inhibitor to preventpolymerization of the unsaturated products, as is well known in the art,may be added at any stage.

III. OXI'DATION 0 F OLEFINS TO NITRILES .a mixture comprising propyleneor isobutylene ammonia and oxygen with the catalyst at an elevatedtemperature and at atmospheric or near atmospheric pressure.

Any source of oxygen may be employed in this process.

"FOI' economic reasons, however, it is preferred that air be employed asthe source of oxygen. From a purely technical viewpoint, relatively puremolecular oxygen will give equivalent results. The molar ratio of oxygento the ole- Efil'l in the feed to the reaction vessel should be in therange of 0.5 l to 4:1 and a ratio of about 1:1 to 3:1 is preferred.

Low molecular weight saturated hydrocarbons do not appear to influencethe reaction to an appreciable degree,

reaction is contemplated within the scope of this invention. Likewise,diluents such as nitrogen and the oxides of carbon may be present in thereaction mixture without deleterious effect.

The molar ratio of ammonia to olefin in the feed to the reaction mayvary between about 0.05 :1 to 5: 1. There is no real upper limit for theammonia-olefin ratio, but there is generally no reason to exceed the 5:1ratio. At ammonia-olefin ratios appreciably less than the stoichiometricratio of 1:1, various amounts of oxygenated derivatives of the olefinwill be formed.

Significant amounts of unsaturated aldehydes as well as nitriles will beobtained at ammonia-olefin ratios substantially below 1:1, i.e., in therange of 0.15:1 to 0.75: 1. Outside the upper limit of this range onlyinsignificant amounts of aldehydes will be produced, and only very smallamounts of nitriles will be produced at ammoniaolefin ratios below thelower limit of this range. It is fortuitous that within theammonia-olefin range stated, maximum utilization of ammonia is obtainedand this is highly desirable. It is generally possible to recycle anyunreacted olefin and unconverted ammonia.

A particularly surprising aspect of this invention is the ettect ofwater on the course of the reaction. We have found that in many caseswater in the mixture fed to the reaction vessel improves the selectivityof the reaction and yield of nitrile. However, reactions not includingwater in the feed are not to be excluded from this invention, inasmuchas water is formed in the course of the reaction.

In general, the molar ratio of added water to olefin, when water isadded, is at least about 0.25: 1. Ratios on the order of 1:1 to 3:1 areparticularly desirable, but higher ratios may be employed, i.e., up toabout :1.

The reaction is carried out at a temperature within the range from about550 to about 1l00 F. The preferred temperatuer range is :from about 800to 1000 F.

The pressure at which reaction is conducted is also an importantvariable, and the reaction should be carried out at about atmospheric orslightly above atmospheric (2 to 3 atmospheres) pressure. In general,high pressures, i.e., about 250 p.s.i.g. are not suitable, since higherpressures tend to favor the formation of undesirable byproducts.

The apparent contact time is not critical, and contact times in therange of from 0.1 to about 50 seconds may be employed. The optimumcont-act time will, of course, vary, depending upon the olefin beingtreated, but in general, a contact time of from 1 to seconds ispreferred.

In general, any apparatus of the type suitable for carrying outoxidation reactions in the vapor phase may be employed in the executionof this process. The process may be conducted either continuously orintermittently. The catalyst bed may be a fixed bed employing a largeparticulate or pelleted catalyst or, in the alternative, a socalledfluidized bed of catalyst may be employed.

The reactor maybe brought to the reaction temperature before or afterthe introduction of the reaction feed mixture. However, in a large scaleoperation, it is preferred to carry out the process in a continuousmanner, and in such a system the recirculation of the unreacted olefinis contemplated. Periodic regeneration or reactivation of the catalystis also contemplated, and this may be accomplished, for example, bycontacting the catalyst with air at an elevated temperature.

The products of the reaction may be recovered by any of the methodsknown to those skilled in the art. One such method involves scrubbingthe efiluent gases from the reactor with cold water or an appropriatesolvent to remove the products of the reaction. If desired, acidifiedwater can be used to absorb the products of reaction and neutralizeunconverted ammonia. The ultimate recovery of the products may beaccomplished by conventional means. The efficiency of the scrubbingoperation may be improved when water is employed as the scrubbing agentby adding a suitable wetting agent to the water. Where molecular oxygenis employed as the oxidizing agent in this process, the resultingproduct mixture remaining after the removal of the nitriles may betreated to remove carbon dioxide with the remainder of .the mixturecontaining the unreacted propylene and oxygen being recycled through thereactor. In the case where air is employed as the oxidizing agent inlieu of molecular oxygen, the residual product after separation of thenitriles and other carbonyl products may be scrubbed with a non-polarsolvent, e.-g., a hydrocarbon fraction, in order to recover unreactedpropylene and in this case the remaining gases may be discarded. Theaddtion of a suitable inhibitor to prevent polymerization of theunsaturated products-during the recovery steps is also contemplated.

The following example, in the opinion of the inventors, representspreferred embodiment of the catalyst system of the invention, and of theprocesses of oxidation of olefins therewith.

Example 1 The following procedure was employed to prepare a catalystcomposed of antimony oxide and cerium oxide having an SbzCe atomic ratioof 10.4 to 1. 45 g. of antimony metal (less than 270 mesh) was oxidizedin 186 cc. of concentrated nitric acid (sp. gr. 1.42) by heating at theboiling point until all red oxides of nitrogen had been given off. Tothis was added 200 cc. of an aqueous solution of 19.6 g. of diammoniumceric nitrate and 150 cc. of 28% ammonium hydroxide. The slurry wasfiltered, and the filter cake Washed with 300 cc., divided into threeportions, of 2.5% ammonium hydroxide solution. Air was drawn through thefilter cake for 15 minutes following the last Washing. The catalyst wasdried overnight at 248 F., calcined at 800 F. for 8 hours, and activatedby heating overnight at 1400 F. in a muifie furnace open to theatmosphere.

The activity of this catalyst in the conversion 0 propylene toacrylonitrile was determined using a micro reactor composed of a feedinduction system, a molten salt bath furnace, sampling valve and vaporphase chromatograph. The reactor was placed in the salt bath furnace,and connected with the feed induction system and sampling device. Thereaction was carried out at a temperature in the range of 880 F., usinga catalyst charge of 3.3 g. The molar ratio of propylene/ammonia/air was1/1/12 and the apparent contact time was 3 seconds. 60.8% of thepropylene feed was converted to acrylonitrile, per pass.

Example 2 The activity of the catalyst for the conversion of propyleneto acrolein was determined using the same apparatus. The reactiontemperature Was 880 F. The molar ratio of propylene/ air was 1/ 10 andthe apparent contact time was 3 seconds. Of the propylene fed, 49.7% wasconverted to acrolein.

We claim:

1. A catalyst composition consisting essentially of oxides of antimonyand cerium as essential catalytic ingredients, the SbzCe atomic ratiobeing within the range from about 1:50 to about 99: 1; the antimony andcerium each being in a valence oxidation state of at least three,resulting from heating of the mixed oxides in the presence of oxygen atan elevated temperature above 500 F. but below their melting point.

2. The catalyst composition in accordance with claim 1 in which theSbzCe atomic ratio is within the range of from about 1:1 .to about 25:1.

3. A catalyst composition in accordance with claim 1,

- activated by further heating at a temperature above and c is a numbertaken to satisfy the average valences .of antimony and cerium in theoxidation states in which they exist in the catalyst; the antimony andcerium each being in a valence oxidation state of at least three, re-

sulting from heating of the mixed oxides in the presence .of oxygen atan elevated temperature above 500 F. but

Sb:Ce atomic ratio being within the range from about 1:50 to about 99:1;said phase being formed by heating the mixed oxides of antimony andcerium in the presence of oxygen at an elevated temperature above500 F.but below their melting point for a time sufiicient to form said phaseof antimony and cerium oxides.

References Cited by the Examiner UNITED STATES PATENTS Bosch et a1. 1252462 XR Lusby 252-462 Bond et al. 252462 Cosby "7-; 26 0-4653 Macleanet a1. 260.465.3

Hadley et a1. 260-604 Baldwin 260-604 Callahan 260-604 Hadley et al.260.465.3 Bethell et'al. 252461 XR 15 MAURICEA. BRINDISI, PrimaryExaminer.

CHARLESB. PARKER, BENJAMIN HENKIN,

Examiners.

1. A CATALYST COMPOSITION CONSISTING ESSENTIALLY OF OXIDES OF ANTIMONYAND CERIUM AS ESSENTIAL CATALYTIC INGREDIENTS, THE SB:CE ATOMIC RATIOBEING WITHIN THE RANGE FROM ABOUT 1:50 TO ABOUT 99:1; THE ANTIMONY ANDCERIUM EACH BEING IN A VALENCE OXIDATION STATE OF AT LEAST THREE,RESULTING FROM HEATING OF THE MIXED OXIDES IN THE PRESENCE OF OXYGEN ATAN ELEVATED TEMPERATURE ABOVE 500*F. BUT BELOW THEIR MELTING POINT.